In recent years, the shift from electric circuits in favor of highly integrated circuits such as LSI etc. has progressed rapidly with the downsizing of electric devices. A multi-pin thin film packaging method of forming contacting terminals, each of which consists of a projected electrode on the upper surface of a support such as a substrate, is applied for mounting LSI etc., on the electric device. In the multi-pin thin film packaging method, a contacting terminal which consists of a bump projecting from the support, or a contacting terminal which consists of a strut called “metal post” projecting from the support and a solder ball formed thereon, and the like are used.
Such a bump and a metal post can be formed by, for example, the following steps: forming a thick resist layer having a thickness of approximately not less than 5 μm on an upper surface of a support having a part made of copper on the upper surface thereof, preferably a copper substrate, exposing the resist layer through a predetermined mask pattern, developing it to remove (strip) selectively the part which forms the contacting terminal, thereby forming a resist pattern, filling the part stripped (non-resist part) with a conductor such as copper, gold, nickel, solder, etc., by plating or the like, and finally removing the resist pattern therearound.
On the other hand, a chemically amplified type resist composition using an acid generator is well known as a highly sensitive photosensitive resin composition. In the chemically amplified type resist composition, an acid is generated from the acid generator by irradiation with radioactive rays. The chemically amplified type resist composition is designed such that the generation of acid is promoted to change the alkali solubility of the base resin contained in the resist composition, when the chemically amplified type resist composition is heated after being exposed. A composition having a characteristic such that the nature of being insoluble in an alkali can be converted to be soluble in an alkali is called “positive type”, whereas a composition having a characteristic such that the nature of being soluble in an alkali can be converted to be insoluble in an alkali is called “negative type”. In this way, the chemically amplified type resist composition acquires a remarkably high photosensitivity superior to that of a conventional resist having a photoreaction coefficient (reaction per 1 photon) of less than 1.
However, hitherto if a photoresist layer is formed on a support which contains copper, using a chemically amplified type resist composition, the copper has the effect of making it difficult to obtain a resist pattern with high accuracy. For example, defects such as film stripping or dropping out may be generated on the resist pattern after being developed.
Patent document 1 (Japanese Unexamined Patent Application, First Publication No. 2003-140347) discloses a technology of laminating a support, and a thick photoresist layer containing a resin of which alkali solubility is changed by an effect of an acid and an acid generator, there being an intervening shielding layer which is constituted from an organic material therebetween for preventing contact between the support and the thick photoresist layer.
However, there is a problem in that the time, the temperature, and the like in the production of the shielding layer must be strictly managed and controlled, because the shielding layer is made from an organic material, and hence the conditions for drying it may differ depending on the thickness, the material, the structure and the like of the under layer of the support.
In addition, mixing of the shielding layer and the photoresist layer may be a problem, in the case in which the shielding layer is made from an organic material. Here, the term “mixing” indicates a phenomenon whereby each of two adjoining layers dissolves to be mixed with each other at the interface therebetween when two or more of layers are laminated.
The present invention was made in view of the above circumstances. It is an object of the present invention to provide a process for forming a resist pattern on a support which has copper on the upper surface thereof, which is capable of reducing the effect of the copper on the resist pattern, easy to control and manage production, and hardly generates the problem of mixing.